In many computers, user input (e.g., cursor control, screen scrolling, etc.) is often achieved by way of a pointing device such as a mouse or a trackball. A typical computer mouse 1 is shown in FIG. 1. Mouse 1 has a case 16 having a bottom case 20 and an upper case 18. As a user slides mouse 1 across a planar (or substantially planar) surface, motion detectors and encoders within case 16 may convert the two-dimensional movement of the mouse across the surface into horizontal and vertical motion of a cursor, pointer, or other object on a computer screen. Mouse 1 has two buttons 8 and 12 which a user can “click” or “double click” to select something on a computer screen. Other mice may have fewer or additional buttons, or other features. Mouse 1 may be connected to a computer or other device by a cord 5 through which mouse 1 may receive power and communicate with a computer (or other device). Alternatively, mouse 1 could be battery powered and communicate via a wireless connection.
Mouse 1 also has a scroll wheel 14. Scroll wheel 14 is located such that the mouse user can comfortably turn the scroll wheel with a finger. The mouse and/or computer may be configured such that turning the wheel causes the screen image to scroll upwards or downwards. The scroll wheel may be configured to perform other functions, such as moving a screen object in a z direction; changing the zoom or other attributes of a screen image; scrolling horizontally; and innumerable other functions. A scroll wheel may also be configured to act as an additional button when pressed by the user.
To prevent the scroll wheel from rotating undesirably (e.g., when the user is moving the mouse but not turning the wheel), to provide a desired tactile sensation for the user, and to provide a means of indexing wheel rotation into discrete increments, some type of restraint is typically imposed on scroll wheel rotation. A common restraint consists of a series of regularly-spaced ridges, detents or other structures on a surface of the wheel or its axis, and a follower biased into contact with the detents. As the wheel rotates, the follower is biased to resist movement out of a detent, and the torque necessary to continue rotating the wheel increases slightly. As the user increases the applied torque (i.e., continues to turn the wheel), the follower rides over a ridge (or other structure separating two detents), whereupon the needed torque decreases until the follower is biased into the next detent. In this way, the user can easily gauge (and make) relatively uniform scrolling movements.
Existing mice scroll wheels restrain wheel rotation through a variety of configurations. U.S. Pat. No. 5,912,661, titled “Z-Encoder Mechanism” and owned by assignee of this invention, describes a configuration in which the detents are located on the axle of the scroll wheel. A metal spring attached to a printed circuit board within the mouse biases a follower into contact with the detents. An improvement upon this configuration is described in U.S. Pat. No. 6,353,429, titled “Detented Optical Encoder” and also owned by the assignee of this invention. Specifically, instead of a metal spring biased into contact with the axle detents, a plastic bracket contacts the axle near one of its rotational hubs and biases the axle upward so as to provide z-switch functionality. A follower, located within the portion of the bracket cradling the axle, is thereby simultaneously biased into contact with the detents. Further improvements are possible, however. For example, the configuration described in the '429 patent requires assembly of at least 4 parts to provide indexed rotation. Because each of these parts (like all mechanical components) will have dimensional tolerances, a “tolerance stack-up” of the assembly results. This tolerance stack-up can potentially result in a rotational torque that may vary from mouse to mouse unless relatively small tolerances are maintained. This can increase manufacturing expense.
In another configuration, regularly-spaced radially-extending indentations are molded into (or otherwise formed in) a side of a scroll wheel in a spoke-like arrangement. A follower piece is biased into contact with the spoke-like indentations on the side of the wheel. The follower piece may be a molded extension of a carriage or other structure supporting a wheel axle, or it may be a separate member that is attached to the carriage. A potential disadvantage of this configuration, however, is the variability in torque required to rotate the wheel in one direction versus the other. In the case of a separate member attached to the carriage, an additional part is required, resulting in additional assembly steps, cost and potential tolerance stacking problems. In yet another configuration, the indentations are not formed in the side of the wheel in a spoke-like arrangement. Instead, a series of ridges and/or depressions are formed on an inner circumference of the wheel. A follower is biased radially outward into contact with the ridges and/or depressions. However, known scroll wheels implementing this configuration utilize a separate biasing member that is not an integral part of the carriage supporting the wheel axle.
A scroll wheel having circumferential detents that are acted upon by a biased follower integrally formed as part of the carriage would result in advantageous savings in assembly steps and expense. Such a design would also facilitate greater control over the fit of the components and allow greater performance consistency among the scroll wheels in different mice. For these and other reasons, advantages can be obtained from further refinements in scroll wheel design.